Field of the Invention
The invention relates to a process for producing a highly purified food ingredient from the extract of the Stevia Rebaudiana Bertoni plant and its use in various food and beverage products.
Description of the Related Art
Nowadays sugar alternatives are receiving increasing attention due to awareness of many diseases in conjunction with consumption of high-sugar foods and beverages. However many artificial sweeteners such as dulcin, sodium cyclamate and saccharin were banned or restricted in some countries due to concerns on their safety. Therefore non-caloric sweeteners of natural origin are becoming increasingly popular. The sweet herb Stevia Rebaudiana Bertoni produces a number of diterpene glycosides which feature high intensity sweetness and sensory properties superior to those of many other high potency sweeteners.
The above-mentioned sweet glycosides, have a common aglycon, steviol, and differ by the number and type of carbohydrate residues at the C13 and C19 positions. The leaves of Stevia are able to accumulate up to 10-20% (on dry weight basis) steviol glycosides. The major glycosides found in Stevia leaves are Rebaudioside A (2-10%), stevioside (2-10%), and Rebaudioside C (1-2%). Other glycosides such as Rebaudioside B, D, E, and F, steviolbioside and rubusoside are found at much lower levels (approx. 0-0.2%).
Two major glycosides—stevioside and Rebaudioside A (Reb A), were extensively studied and characterized in terms of their suitability as commercial high intensity sweeteners. Stability studies in carbonated beverages confirmed their heat and pH stability (Chang S. S., Cook, J. M. (1983) Stability studies of stevioside and Rebaudioside A in carbonated beverages. J. Agric. Food Chem. 31: 409-412.)
Steviol glycosides differ from each other not only by molecular structure, but also by their taste properties. Usually stevioside is found to be 110-270 times sweeter than sucrose, Rebaudioside A between 150 and 320 times, and Rebaudioside C between 40-60 times sweeter than sucrose. Dulcoside A is 30 times sweeter than sucrose. Rebaudioside A has the least astringent, the least bitter, and the least persistent aftertaste thus possessing the most favorable sensory attributes in major steviol glycosides (Tanaka O. (1987) Improvement of taste of natural sweeteners. Pure Appl. Chem. 69:675-683; Phillips K. C. (1989) Stevia: steps in developing a new sweetener. In: Grenby T. H. ed. Developments in sweeteners, vol. 3. Elsevier Applied Science, London. 1-43). The chemical structure of Rebaudioside A is shown in FIG. 1.
Methods for the extraction and purification of sweet glycosides from the Stevia Rebaudiana plant using water or organic solvents are described in, for example, U.S. Pat. Nos. 4,361,697; 4,082,858; 4,892,938; 5,972,120; 5,962,678; 7,838,044 and 7,862,845.
However, even in a highly purified state, steviol glycosides still possess non-sweet taste attributes such as bitterness, sweet aftertaste, licorice flavor, etc. One of the main obstacles for the successful commercialization of stevia sweeteners are such non-sweet taste attributes. It was shown that these flavor notes become more prominent as the concentration of steviol glycosides increases (Prakash I., DuBois G. E., Clos J. F., Wilkens K. L., Fosdick L. E. (2008) Development of Rebiana, a natural, non-caloric sweetener. Food Chem. Toxicol., 46, S75-S82.).
Rebaudioside B (CAS No: 58543-17-2), or Reb B, also known as stevioside A4 (Kennelly E. J. (2002) Constituents of Stevia Rebaudiana In Stevia: The genus Stevia, Kinghorn A. D. (Ed), Taylor & Francis, London, p.71), is one of the sweet glycosides found in Stevia Rebaudiana. Sensory evaluations show that Reb B was approximately 300-350 times sweeter than sucrose, while for Reb A this value was approximately 350-450 (Crammer, B. and Ikan, R. (1986) Sweet glycosides from the Stevia plant. Chemistry in Britain 22, 915-916, and 918). The chemical structure of Rebaudioside B is shown in FIG. 2a. 
It was believed that Reb B forms from partial hydrolysis of Rebaudioside A during the extraction process (Kobayashi, M., Horikawa, S., Degrandi, I. H., Ueno, J. and Mitsuhashi, H. (1977) Dulcosides A and B, new diterpene glycosides from Stevia Rebaudiana. Phytochemistry 16, 1405-1408). However further research shows that Reb B occurs naturally in the leaves of Stevia Rebaudiana and currently it is one of nine steviol glycosides recognized by FAO/JECFA (United Nations' Food and Agriculture Organization/Joint Expert Committee on Food Additives) in calculating total steviol glycosides' content in commercial steviol glycosides preparations (FAO JECFA (2010) Steviol Glycosides, Compendium of Food Additive Specifications, FAO JECFA Monographs 10, 17-21).
It is also noted that no significant work has been conducted to determine the potential of Reb B as a sweetener or food ingredient. Moreover Reb B is often viewed as process artifact and unnecessary impurity in commercial steviol glycosides preparations. No significant evaluation of Reb B influence on overall taste profile of steviol glycosides preparations has been conducted.
In food and beverage applications, the solubility of high intensity sweeteners like steviol glycosides is very important and can be a significant barrier to achieve the desirable sweetness and taste profile. However highly purified steviol glycosides possess relatively low water solubility. For example Rebaudioside A (Reb A) thermodynamic equilibrium solubility at room temperature is only 0.8%. On the other hand, the water solubility of Reb B is reported to be about 0.1% and that of Reb D (FIG. 2b) is even lower, only at 0.01-0.05% at room temperature (Kinghorn A. D. (2002) Constituents of Stevia Rebaudiana In Stevia: The genus Stevia, Kinghorn A. D. (Ed), Taylor & Francis, London, p.8). Reb B or Reb D can be solubilized at higher concentrations at a higher temperature, but they will quickly crystallize back from solution upon cooling to room temperature. Considering high sweetness intensity of steviol glycosides (100-300 times of sugar sweetness)—even 0.05% solubility may seem sufficient for many applications.
In many food processes where highly concentrated ingredients are used, a highly soluble form of Reb B and Reb D will be necessary.
Considering the facts mentioned above, it is necessary to evaluate Reb B as a sweetener and food ingredient and develop a simple and efficient process for food grade Reb B preparations suitable for food applications.